Polysaccharides are important biological molecules and they have been widely used in the pharmaceutical industry for the prevention and treatment of diseases. For example, capsular polysaccharides have been used for many years in vaccines against capsulated bacteria, such as meningococcus (Neisseria meningitidis), pneumococcus (Streptococcus pneumoniae) and Hib (Haemophilus influenzae type B).
To enhance immunogenicity of these polysaccharides, particularly in children, conjugate vaccines were developed. These comprise a capsular polysaccharide conjugated to a carrier protein [e.g. U.S. Pat. Nos. 4,711,779, 4,761,283 and 4,882,317]. The conjugated molecule may have the polysaccharide and protein linked directly or the polysaccharide and protein may be linked via a linker moiety.
Whilst different types of linker moieties have been developed, there is a need for new types of linker which are versatile and which can be coupled to the polysaccharide and protein using simple, reliable chemistry. There is a further need for new linkers which are non-toxic and which can be formed under mild conditions, avoiding the use of harsh reagents, such as strong acids and bases.